Aluminum alloy for die casting and aluminum-alloy die cast obtained therefrom

ABSTRACT

Provided are: an aluminum alloy for die casting, having castability equivalent to that of ADC 12  and having high yield strength and high ductility; and an aluminum alloy die cast obtained through die-casting the alloy. That is, the aluminum alloy for die casting according to the present invention contains: Si by more than 6.00 wt % and less than 6.50 wt %; Mg by 0.10 to 0.50 wt %; Fe by not more than 0.30 wt %; Mn by 0.30 to 0.60 wt %; Cr by 0.10 to 0.30 wt %; and Al and unavoidable impurities as a remaining portion of the aluminum alloy.

TECHNICAL FIELD

The present invention relates to an aluminum alloy for die castinghaving improved yield strength and ductility, and an aluminum alloy diecast produced using the alloy.

BACKGROUND ART

Aluminum alloys are lightweight and are excellent in moldability andmass productivity, and therefore are widely used as materials forcomponents in various fields such as automobiles, industrial machines,aircrafts, and electrical home appliances.

For use in automobiles, many components using aluminum alloys areadopted for the purpose of reducing the weight of an automobile body.Meanwhile, with increase in the number of components for which use ofaluminum alloys is considered, existing aluminum alloys cannot satisfymechanical properties required of these components in some cases.

Under such circumstances, as a technology for solving the above problem,for example, Patent Literature 1 described below discloses an aluminumalloy for casting that contains: silicon by 5.0 to 11.0%; magnesium by0.2 to 0.8%; chromium by 0.3 to 1.5%; and iron by not more than 1.2%,and that has a high elongation percentage, as a material suitable forcomponents requiring high elongation, such as disc wheels ofautomobiles.

According to this technology, it is possible to provide an aluminumalloy for casting that has high elongation while containing iron as animpurity.

CITATION LIST Patent Literature

[PTL 1] Japanese Laid-Open Patent Publication No. S52-126609

SUMMARY OF INVENTION Technical Problem

However, in the above-described conventional technology, it is notcertain whether the aluminum alloy is applicable to components requiringhigher elongation and high yield strength, such as engine mounts, and itis difficult to say that the aluminum alloy has suitability for diecasting that enables mass production of fine components such as enginemounts.

Thus, a main objective of the present invention is to provide: analuminum alloy for die casting having castability equivalent to that ofADC12 that is an Al—Si—Cu based alloy for die casting specified byJapanese Industrial Standards JIS H5302 (hereinafter simply referred toas “ADC12”), and having high yield strength and high ductility; and analuminum alloy die cast produced using the alloy.

Solution to Problem

A first aspect of the present invention is an aluminum alloy for diecasting containing: Si by more than 6.00 wt % and less than 6.50 wt %;Mg by 0.10 to 0.50 wt %; Fe by not more than 0.30 wt %; Mn by 0.30 to0.60 wt %; Cr by 0.10 to 0.30 wt %; and Al and unavoidable impurities asa remaining portion of the aluminum alloy.

In this aspect, Si is contained as a main component by more than 6.00 wt% and less than 6.50 wt % to minimize reduction in elongation whilemaintaining fluidity during die casting, and the content ratio of Fe,which significantly affects elongation of the alloy, is reduced to notmore than 0.30 wt %, and further, Mn, which has an effect to improveanti-seizing characteristic and elongation of the alloy during diecasting, is contained by 0.30 to 0.60 wt %. Therefore, it is possible toobtain an alloy having: suitability for die casting equivalent to thatof ADC12; yield strength equivalent to that of ADC12; and elongationsignificantly higher than that of ADC12.

As described above, in the present invention, by simply containing thefive types of elemental components at the predetermined ratio, an ingotof an aluminum alloy for die casting having not only excellentcastability for die casting but also excellent mechanical properties,especially elongation (ductility) and yield strength, can be producedsafely and easily.

With respect to the aluminum alloy for die casting according to thepresent invention, preferably, at least one selected from Na, Sr, and Cais added by 30 to 200 ppm, or Sb is added by 0.05 to 0.20 wt %. By doingso, it is possible to reduce the size of particles of eutectic Si andfurther improve strength and toughness of the aluminum alloy.

In addition, adding Ti by 0.05 to 0.30 wt % or adding B by 1 to 50 ppmis also preferable. By doing so, crystal grains of the aluminum alloycan be miniaturized even when the amount of Si is particularly small orwhen a casting method having a low cooling rate is used. As a result,elongation of the aluminum alloy can be improved.

A second aspect of the present invention is an aluminum alloy die castobtained through die-casting the aluminum alloy for die castingaccording to the first aspect.

Since the aluminum alloy die cast obtained through die-casting thealuminum alloy for die casting according to the present invention can bemass produced with satisfactory castability and is superior in yieldstrength and elongation, the aluminum alloy die cast is most suitablefor structural components for automobiles, especially components such asengine mounts.

Advantageous Effects of Invention

According to the present invention, it is possible to provide: analuminum alloy for die casting, having castability equivalent to that ofADC12 and high yield strength and high ductility; and an aluminum alloydie cast produced using the alloy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows graphs representing the relationships between the amount ofMn in aluminum alloys for die casting according to Examples andComparative Examples of the present invention, and mechanical propertiesof the alloys, in which FIG. 1(a) represents the relationship betweenthe amount of Mn and elongations of the alloys, and FIG. 1(b) representsthe relationship between the amount of Mn and 0.2%-yield strengths ofthe alloys.

DESCRIPTION OF EMBODIMENTS

In the following, an embodiment of the present invention will bedescribed in detail with specific examples.

An aluminum alloy for die casting of the present invention (hereinafter,also simply referred to as “aluminum alloy”) mainly contains: Si(silicon) by more than 6.00 wt % and less than 6.50 wt %; Mg (magnesium)by 0.10 to 0.50 wt %; Fe (iron) by not more than 0.30 wt %; Mn(manganese) by 0.30 to 0.60 wt %; Cr (chromium) by 0.10 to 0.30 wt %;and Al (aluminum) and unavoidable impurities as a remaining portion ofthe aluminum alloy. Hereinafter, the properties of each of the elementswill be described.

Si (silicon) is an important element that contributes to improvement offluidity, reduction in liquidus temperature, and the like when thealuminum alloy is molten, thereby to improve castability.

The content ratio of Si with respect to the whole weight of the aluminumalloy is preferably within a range of more than 6.00 wt % and less than6.50 wt % as described above. When the content ratio of Si is not morethan 6.00 wt %, melting temperature and casting temperature of thealuminum alloy increase, and sufficient fluidity cannot be ensuredduring die casting since fluidity of the aluminum alloy reduces when thealuminum alloy is molten. On the other hand, when the content ratio ofSi is more than 6.50 wt %, elongation of the obtained alloy is reducedalthough sufficient fluidity can be ensured during die casting.

Mg (magnesium) mainly exists as Mg₂Si or in a solid-solution state in anAl base material in the aluminum alloy, and is a component that provides0.2%-yield strength and tensile strength to the aluminum alloy, but,when being contained by an excessive amount, has an adverse effect oncastability and elongation of the alloy.

The content ratio of Mg with respect to the whole weight of the aluminumalloy is preferably within a range of 0.10 to 0.50 wt % as describedabove. The presence of Mg within the above range can improve mechanicalproperties of the aluminum alloy such as yield strength and tensilestrength, without greatly affecting castability and elongation of thealloy. When the blending ratio of Mg is more than 0.50 wt %, elongationof the alloy is reduced, which results in degraded quality of analuminum alloy die cast produced by using the alloy.

Fe (iron) is known to have a seizing prevention effect during diecasting. However, Fe causes crystallization of a needle like crystal inthe form of Al—Si—Fe, significantly reduces elongation of the aluminumalloy, and, when being added in a large quantity, causes melting at asuitable temperature to be difficult.

The content ratio of Fe with respect to the whole weight of the aluminumalloy is preferably not more than 0.30 wt % as described above. When thecontent ratio of Fe is more than 0.30 wt %, elongation of the alloy isremarkably reduced although the seizing prevention effect is sufficient.

Mn (manganese) is used mainly for preventing seizing of the aluminumalloy and a mold during casting.

The blending ratio of Mn with respect to the whole weight of thealuminum alloy is preferably within a range of 0.30 to 0.60 wt % asdescribed above, and more preferably within a range of 0.40 to 0.60 wt%. When the blending ratio of Mn is less than 0.30 wt %, seizing willoccur between the aluminum alloy and a mold during die casting. On theother hand, when the blending ratio of Mn is more than 0.60 wt %,elongation of the alloy is reduced although the problem of seizing doesnot occur during die casting.

In the aluminum alloy of the present invention, since the blending ratioof Mn up to 0.60 wt % is accepted with respect to the weight of thewhole alloy as described above, an Al—Mn based scrap having high Mncontent, as in the case with aluminum can recycled materials, can beused as a part of the raw material for the alloy.

Cr (chromium) mainly exists in a molten state when the aluminum alloy ismolten, and when the aluminum alloy is solid, exists in a solid-solutionstate in an Al phase or in a crystallized state as an Al—Si—Cr phase oran Al—Si—Cr—Fe phase. Cr is used for preventing seizing of the aluminumalloy and a mold during die casting.

The blending ratio of Cr with respect to the whole weight of thealuminum alloy is preferably within the range of 0.10 to 0.30 wt % asdescribed above. When the blending ratio of Cr is less than 0.10 wt %,seizing will occur between the aluminum alloy and a mold during diecasting. On the other hand, when the blending ratio of Cr is more than0.30 wt %, elongation of the aluminum alloy is rapidly reduced althoughseizing during die casting is solved.

When the content ratios of Si, Mg, Fe, Mn, and Cr are adjusted inaccordance with the content ratios described above, it is possible toobtain a base metal of an aluminum alloy for die casting havingcastability equivalent to that of ADC12, and having high yield strengthand high ductility.

In the above-described aluminum alloy for die casting in an as-caststate, elongation (breaking elongation) thereof is preferably not lessthan 11%, and at the same time, 0.2%-yield strength thereof ispreferably not less than 125 MPa. An aluminum alloy for die castinghaving such mechanical properties is particularly suitable as a die-castmaterial for engine mounts of automobiles.

In addition to the elemental components described above, at least oneelement selected from Na (sodium), Sr (strontium), Ca (calcium), and Sb(antimony) may be added as a modification material. By adding such amodification material, it is possible to reduce the size of eutectic Siparticles, and further improve toughness and strength of the aluminumalloy.

The addition ratio of the modification material with respect to thewhole weight of the aluminum alloy is preferably within a range of 30 to200 ppm when the modification material is Na, Sr, and Ca, and within arange of 0.05 to 0.20 wt % when the modification material is Sb. Whenthe addition ratio of the modification material is less than 30 ppm(0.05 wt % in the case with Sb), miniaturizing eutectic Si particles inthe aluminum alloy becomes difficult, whereas when the addition ratio ofthe modification material is more than 200 ppm (0.20 wt % in the casewith Sb), eutectic Si particles in the aluminum alloy are sufficientlyminiaturized, and no further addition effect can be obtained even whenthe added amount is increased.

Furthermore, at least one of Ti (titanium) and B (boron) may be addedinstead of or together with the modification material. By adding atleast one of Ti and B in such manner, crystal grains of the aluminumalloy are miniaturized, and elongation of the alloy can be improved. Itshould be noted that such an advantageous effect becomes significantwhen the amount of Si is particularly small or when a casting methodhaving a low cooling rate is used.

The addition ratios of Ti and B with respect to the whole weight of thealuminum alloy are preferably within a range of 0.05 to 0.30 wt % and arange of 1 to 50 ppm, respectively. When the addition ratio of Ti isless than 0.05 wt % or the addition ratio of B is less than 1 ppm,miniaturizing the crystal grains in the aluminum alloy becomesdifficult, whereas when the addition ratio of Ti is more than 0.30 wt %or the addition ratio of B is more than 50 ppm, the crystal grains inthe aluminum alloy are sufficiently miniaturized, and no furtheraddition effect can be obtained even when the added amount is increased.

When the aluminum alloy for die casting according to the presentinvention is to be produced, first, a raw material designed to contain,at the predetermined ratio described above, each of the elementalcomponents of Al, Si, Mg, Fe, Mn, and Cr is prepared. Next, the rawmaterial is placed in a melting furnace such as a sealed melting furnaceor a melting furnace with a fore hearth to melt the raw material. Themolten raw material, i.e., the molten metal of the aluminum alloy issubjected to refinement treatments such as a dehydrogenation treatmentand an inclusion removal treatment, if necessary. Then, the refinedmolten metal is casted in a predetermined mold and solidified in orderto form the molten metal of the aluminum alloy into an alloy base metalingot or the like.

Furthermore, after producing the aluminum alloy die cast using thealuminum alloy for die casting according to the present invention, asolution treatment and an aging treatment, etc., are performed ifnecessary. By performing the solution treatment and the aging treatmenton the aluminum alloy die cast in such manner, mechanical properties ofthe aluminum alloy cast can be improved.

EXAMPLES

In the following, the present invention will be described specificallyby means of Examples, but the present invention is not limited to theExamples.

Mechanical properties (tensile strength, elongation, and 0.2%-yieldstrength) in predetermined Examples and Comparative Examples weremeasured by a method described below. Specifically, by using an ordinarydie casting machine (DC135EL manufactured by Toshiba Machine Co., Ltd.)having a clamping force of 135 ton, die casting was performed at aninjection speed of 1.0 m/s with a casting pressure of 60 MPa to producea round bar test piece that is in compliance with ASTM (American Societyfor Testing and Material) standard. Then, tensile strength, elongation(breaking elongation), and 0.2%-yield strength were measured for theround bar test piece in an as-cast state by using a universal testingmachine (AG-IS 100kN) manufactured by Shimadzu Corp.

A solid emission spectrophotometer (Thermo Scientific (registeredtrademark) ARL 4460) manufactured by Thermo Fisher Scientific Inc. wasused for component analysis of the round bar test piece produced by diecasting.

Further, in order to evaluate castability of each alloy, fluidity of themolten metal and presence/absence of seizing to a mold (anti-seizingcharacteristic) during the die casting were visually observed, and wereevaluated in three grades of ∘ (good), Δ (fair), x (poor).

Table 1 shows elemental compositions, mechanical properties, andsuitabilities for die casting of aluminum alloys, which are the objectsof the present invention, in Examples 1 and 2 and Comparative Examples 1to 3. Comparative Example 1 corresponds to ADC12 that is widely used asan aluminum alloy for die casting.

TABLE 1 Table 1-(1). Elemental compositions of Examples and ComparativeExamples Elemental composition (wt %) Cu Si Mg Fe Mn Cr Example 1 0.006.17 0.35 0.19 0.41 0.20 Example 2 0.01 6.24 0.36 0.19 0.60 0.20Comparative Example 1 1.79 10.41 0.27 1.28 0.19 0.04 Comparative Example2 0.01 6.24 0.34 0.19 0.01 0.20 Comparative Example 3 0.01 6.21 0.350.19 0.21 0.20 Table 1-(2). Physical property measurement results andcastability evaluation results of Examples and Comparative ExamplesPhysical property measurement result Tensile 0.2%-yield strengthElongation strength Anti-seizing (MPa) (%) (MPa) Fluidity characteristicExample 1 274 11.9 126 ∘ ∘ Example 2 280 11.9 127 ∘ ∘ Comparative 3132.4 155 ∘ ∘ Example 1 Comparative 265 11.1 117 ∘ x Example 2 Comparative273 11.4 123 ∘ Δ Example 3

According to Table 1, when Examples 1 and 2, which are alloys of thepresent invention, are compared with Comparative Example 1 correspondingto ADC12, it is found that elongations of the alloys of Examples 1 and 2are significantly higher than that of Comparative Example 1corresponding to ADC12 although both have equivalent castability (i.e.,suitability for die casting).

Further, when Examples 1 and 2 are compared with Comparative Examples 2and 3 in which only the content ratios of Mn are different from those ofExamples 1 and 2, it is found from FIG. 1 and Table 1 that, with 0.3 wt% of Mn being a boundary, Examples 1 and 2 containing more than 0.3 wt %of Mn are able to effectively prevent seizing during die casting, andhave improved elongations and 0.2%-yield strengths of the alloys.

1. An aluminum alloy for die casting comprising: Si by more than 6.00 wt% and less than 6.50 wt %; Mg by 0.10 to 0.50 wt %; Fe by not more than0.30 wt %; Mn by 0.30 to 0.60 wt %; Cr by 0.10 to 0.30 wt %; and Al andunavoidable impurities as a remaining portion of the aluminum alloy. 2.The aluminum alloy for die casting according to claim 1, wherein atleast one selected from Na, Sr, and Ca is added by 30 to 200 ppm.
 3. Thealuminum alloy for die casting according to claim 1, wherein Sb is addedby 0.05 to 0.20 wt %.
 4. The aluminum alloy for die casting according toclaim 1, wherein Ti is added by 0.05 to 0.30 wt %.
 5. The aluminum alloyfor die casting according to claim 1, wherein B is added by 1 to 50 ppm.6. An aluminum alloy die cast obtained through die-casting the aluminumalloy for die casting according to claim 1.